Advanced Very High Resolution Radiometer - AVHRR

Archive Header

Delivery option that allows the user to specify whether or not the ordered data will include an archive header. In particular, for data from NOAA-14 and earlier NOAA satellites, the archive header is the TBM (Tera Byte Memory) header which is described in the NOAA Polar Orbiter Data User's Guide located at http://www2.ncdc.noaa.gov/docs/podug/index.htm For data from NOAA-15 and later NOAA satellites, the archive header is the ARS (Archive Retrieval System) header which is described in the NOAA KLM User's Guide located at http://www2.ncdc.noaa.gov/docs/klm/

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Bits/Pixel

User option for the data delivery format. Indicates the number of bits to be used to represent each sensor pixel value in the delivery file. Choosing 8 or 16 bits/pixel results in the unpacking of the sensor data and the placing of each pixel value into the indicated number of bits. Note that the sensor data originates in a packed format with each pixel value occupying 10 bits. If 8 is chosen, the least significant of the original 10 bits are discarded. If 16 is chosen, the original 10 bits are preserved and are packed into a 16-bit word. Choosing 8 or 16 bits/pixel also allows users to select which combination of channels they want in their delivery files. Choosing 10 bits/pixel results in the data being delivered in the original packed format with all 5 channels. Users cannot perform channel selection if they choose 10 bits/pixel.

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Channel Number

User option for the data delivery format. The channel number, or band, of the instrument that acquired the data. Channel numbers are associated with different wavelengths or ranges of wavelengths within the electromagnetic spectrum. Users may choose which combination of channels they wish to receive in their delivery files if, and only if, they choose either 8 or 16 for the bits/pixel value.

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Data Usage Guidance/Restrictions

The operational data for this datatype is available to all registered CLASS users. Pre-operational data may be restricted to authorized users. To become an authorized user, send a request to the CLASS Help Desk.

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Dataset Name

The name of the Level 1B data set archived at CLASS.
The name has the following format: Processing-Center.Data-Type.Spacecraft-Unique-ID.Year-Day.Start-Time.Stop-Time.Processing-Block-ID.Source with each qualifier defined below:

Qualifier Details
Processing-Center Three characters identifying where the data was created. Recognized character groups are:
CMS = Centre de Meteorologie Spatiale/France
DSS=Dundee Satellite Receiving Station - Dundee, Scotland, UK
NSS = NOAA/NESDIS - Suitland, Maryland, USA
UKM = United Kingdom Meteorological Office - Bracknell, England, UK
Data-Type Four characters identifying the data type and transmission method. Recognized character groups are:
HRPT= HRPT (direct readout full resolution AVHRR)
GHRR= GAC (recorded reduced resolution AVHRR)
LHRR= LAC (recorded HRPT AVHRR)
Spacecraft-Unique-ID TN = TIROS-N
NA = NOAA-6 (aka NOAA-A)
NB = NOAA-B
NC = NOAA-7 (NOAA-C)
ND = NOAA-12 (NOAA-D)
NE = NOAA-8 (NOAA-E)
NF = NOAA-9 (NOAA-F)
NG = NOAA-10 (NOAA-G)
NH = NOAA-11 (NOAA-H)
NJ = NOAA-14 (NOAA-J)
NK = NOAA-15 (NOAA-K)
NL = NOAA-16 (NOAA-L)
NM = NOAA-17 (NOAA-M)
NN = NOAA-18 (NOAA-N)
NP = NOAA-19 (NOAA-NPrime)
Year-Day e.g. D79104, where "D" identifies this group as a Julian day delimiter, "79" identifies the year in which the spacecraft began recording the data set and "104" identifies the Julian day on which the spacecraft began recording the data set.
Start-Time e.g. S1355, where "S" identifies this group as a start time delimiter. "1355" denotes 13 hours 55 minutes UTC (to the nearest minute) and represents the time at which spacecraft recording began.
Stop-Time e.g. E1456, where "E" identifies this group as an end time delimiter. "1456" denotes 14 hours 56 minutes UTC (to the nearest minute) and denotes the time of spacecraft recording of the last usable data in the data set.
Processing-Block-ID e.g. B0016465, where "B" identifies this group as a processing block ID delimiter. "0016465" is a seven digit number identifying the spacecraft revolution (orbit) in which recording of this data set began and the revolution in which the recording of the data set ended (the first five digits identifying the beginning revolution and the last two being the
two least significant digits of the ending revolution).
Source Two characters identifying data acquisition source. Valid character groups are:
DU = Dundee, Scotland, UK
GC = Fairbanks, Alaska, USA (formerly Gilmore Creek)
HO = Honolulu, Hawaii,
USAMO = Monterey, California,
USASO = Satellite Operations Control Center, Suitland, Maryland,
USAWE = Western Europe, Lannion, France
WI = Wallops Island, Virginia, USA

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Datatype

The data types available for AVHRR are:

Full Resolution Area Coverage (FRAC): AVHRR FRAC data, the user may choose 1 km or 4 km as their default, available in swaths typically covering roughly an orbits worth of data. FRAC data is available for all areas of the globe and is available for data from the METOP satellites.

Global Area Coverage (GAC): AVHRR data at the reduced 4KM resolution, available in swaths typically covering roughly an orbits worth of data. GAC data is available for all areas of the globe.

High Resolution Picture Transmission (HRPT): Limited area AVHRR data at the full 1KM resolution, available in swaths typically covering roughly 12 minutes worth of an orbit. HRPT data is only available for areas of the earth scanned by the sensor while the satellite is within range of a receiving station.

Local Area Coverage (LAC): Limited area AVHRR data at the full 1KM resolution, available in swaths typically covering roughly 12 minutes worth of data. LAC data is recorded on-board the satellite and transmitted to a receiving station once the satellite is within range of the station. Because of limitations in the amount of data that can be stored on the satellites recorders, LAC data is limited and the acquisition of the data is scheduled.

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End Time

The UTC date and time corresponding to the end of the coverage of the given dataset. Format is yyyy-mm-dd hh:mm:ss.fff where fff is the fraction of a second in milliseconds.

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Inventory ID

A unique numerical ID assigned to the data set for CLASS inventory purposes.

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Node

The ascending node refers to that portion of the orbit during which the satellite is heading northward. Descending refers to the southbound portion.

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Orbit

The number of the orbit (revolution) in which the satellite was traveling when the data was acquired.

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Quality

Flags indicating data quality.

Character Position Meaning
1 G = gaps were present in the data set
N = no gaps were found
X = data set was not verified for gaps
2 B = both the start and end times were adjusted
S = start time was adjusted
E = end time was adjusted
N = neither time was adjusted
X = data set was not verified for times
3 Reserved for future use

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Receiving Station

The ground station to which data was transmitted for the given data set.

Two characters at end of 1B data set name Receiving Station
DU Dundee, Scotland, UK
GC Fairbanks, Alaska, USA (formerly Gilmore Creek)
HO Honolulu, Hawaii, USA
MO Monterey, California, USA
SO Satellite Operations Control Center, Suitland, Maryland, USA (SOCC)
WE Western Europe, Lannion, France
WI Wallops Island, Virginia, USA

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Resolution

For LAC and HRPT, the instantaneous field-of-view (IFOV) of each channel is approximately 1.4 milliradians (mr) leading to a resolution at the satellite subpoint of 1.1 km for a nominal altitude of 833 km. This is generally referred to as 1 km resolution. Since GAC data contain only one out of three original AVHRR lines and the data volume and resolution are further reduced by averaging every four adjacent samples and skipping the fifth sample along the scan line, the effective resolution is 1.1 x 4 km with a 3 km gap between pixels across the scan line. This is generally referred to as 4 km resolution.

Satellite

The satellite that acquired the AVHRR data.

TN TN TIROS-N
N06 NA NOAA-6
N07 NC NOAA-7
N08 NE NOAA-8
N09 NF NOAA-9
N10 NG NOAA-10
N11 NH NOAA-11
N12 ND NOAA-12
N14 NJ NOAA-14
N15 NK NOAA-15
N16 NL NOAA-16
N17 NM NOAA-17
N18 NN NOAA-18
N19 NP NOAA-19

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Scan Line Selection

User option for the data delivery format. If a user chooses this option, the delivery file will contain all scans meeting the search criteria used to obtain the given data set as a hit. If the user deselects this option, the delivery file will contain all scans contained within the given data set.

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Size

The size of the file to be delivered to the user in bytes.

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Spatial

Refers to the geographic area of interest to the user. This section of the search page allows the user to define the geographic area of interest.

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Start Time

The UTC date and time corresponding to the beginning of the coverage of the given dataset. Format is yyyy-mm-dd hh:mm:ss.fff where fff is the fraction of a second in milliseconds.

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Temporal

Refers to the time span of interest to the user. This section of the search page allows the user to define the range of dates/times of interest.

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UTC

Coordinated Universal Time (UTC) is the international time standard. It is the current term for what was referred to as Greenwich Meridian Time (GMT). Zero (0) hours UTC is midnight in Greenwich England, which lies on the zero longitudinal meridian. Universal time is based on a 24 hour clock, therefore, afternoon hours such as 4 pm UTC are expressed as 16:00 UTC (sixteen hours, zero minutes).

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